As a next-generation communication system of the W-CDMA (Wideband Code Division Multiple Access) system and the HSDPA (High Speed Downlink Packet Access) system, an E-UTRA (Evolved UTRA and UTRAN) system (also referred to as an LTE (Long Term Evolution) system or a Super 3G system) has been studied by 3GPP (3rd Generation Partnership Project) which is a standards body of the W-CDMA. In the E-UTRA system, an OFDMA (Orthogonal Frequency Division Multiple Access) scheme and an SC-FDMA (Single-Carrier Frequency Division Multiple Access) scheme are applied to downlink communications and uplink communications, respectively.
The OFDMA scheme is a transmission scheme in which a frequency band is divided into plural subcarriers having narrower frequency bands and data are transmitted on the respective subcarriers. In the OFDMA scheme, the subcarriers are closely arranged in the frequency direction, allowing the subcarriers to be partly overlapped without causing interference, so that fast data transmission can be achieved and frequency usage efficiency can be improved.
The SC-FDMA scheme is a transmission scheme in which a frequency band is divided so that different frequencies can be separately used among plural terminals (user equipment terminals) and as a result, interference between terminals can be reduced. Further, in the SC-FDMA scheme, a range of transmission power fluctuation can be made smaller, and thus lower energy consumption of terminals can be achieved and a wider coverage area can be obtained.
The SC-FDMA scheme used for uplink radio access in the E-UTRA system is described below. A frequency band available for the system is divided into plural resource blocks. Each resource block includes one or more subcarriers. One or more resource blocks are allocated to a user equipment (UE) terminal. According to frequency scheduling, a base station apparatus preferentially allocates resource blocks to user equipment terminals having better channel conditions based on received signal quality or channel condition information (CQI: channel quality indicator), which is measured by the base station apparatus, for each uplink resource block for each user equipment terminal. As a result, transmission efficiency or throughput in the whole system can be improved. In addition, frequency hopping may be used to change available frequency blocks according to a predetermined frequency hopping pattern.
In the SC-FDMA scheme, respective user equipment terminals in a cell transmit signals using different time and frequency resources. Thus, orthogonality among user equipment terminals in the cell can be achieved. In the SC-FDMA scheme, a continuous frequency is allocated to the user equipment terminal, thereby allowing for single-carrier transmissions with low PAPR (peak-to-average power ratio). Accordingly, a wider coverage area can be obtained in uplink with severe restrictions on transmission power. In the SC-FDMA scheme, time and frequency resources to be allocated are determined by the scheduler in the base station apparatus based on a propagation condition and/or QoS (Quality of Service) of data to be transmitted for each user. As used herein, the QoS includes a data rate, a required error rate, and a delay. Allocating time and frequency resources to respective user equipment terminals with better propagation conditions in this manner can improve throughput.
[Non-patent document 1] 3GPP TS 36.211: “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation”.